The six research projects that are components of this program will continue studies of nerve cell properties using physiological, anatomical and biochemical approaches. The main emphasis in the projects will be on the mechanisms of cell interaction, including synaptic interaction of neurons with one another and with other targets, and long-term interaction of neurons with other types of cells. The systems being studied include amphibian and mammalian sympathetic ganglia, lobster neurons, barnacle photoreceptor cells and second-order visual neurons, and insect sensory systems. Interaction mechanisms are being studied both in vivo and in culture; the development of synaptic mechanisms is a central aspect of several of the projects. Questions that are being addressed are: 1). What factors regulate the determination and differentiation of neuronal transmitter systems in mammalian sympathetic neurons; 2). What are the mechanisms and functional significance of very slow synaptic events in amphibian sympathetic ganglia; 3). What are the mechanisms and significance of the modulation of synaptic and contractile events caused by biogenic amines in crustacean nerve-muscle systems; 4). How do transmitter systems and neuronal connections develop during metamorphosis in an insect; 5). What are the early steps in the processing of visual information, from photoreceptors to second-order neurons, in a grant barnacle.